Exploiting super peers for large-scale peer-to-peer Wi-Fi roaming

Exploiting super peers for large-scale peer-to-peer Wi-Fi roaming

Exploiting super peers for large-scale peer-to-peer Wi-Fi roamingEfstratios G. Dimopoulos, Pantelis A. Frangoudis and George.C.PolyzosEfstratios G. Dimopoulos, Pantelis A. Frangoudis and George.C.Polyzos

MotivationMotivation

Very high Wi-Fi density in cities The case for Skyhook Residential Wi-Fi hotspots with excess

capacity How to exploit this user-provided

infrastructure? We need a Wi-Fi sharing scheme! Can community based Wi-Fi access

complement cellular?

Very high Wi-Fi density in cities The case for Skyhook Residential Wi-Fi hotspots with excess

capacity How to exploit this user-provided

infrastructure? We need a Wi-Fi sharing scheme! Can community based Wi-Fi access

complement cellular?2

Design optionsDesign options

Centralized Permanent IDs Full view of

transactions Easy to detect

misuse

FON

Centralized Permanent IDs Full view of

transactions Easy to detect

misuse

FON

3

Decentralized Free/disposable IDs Enhances privacy Should discourage

misuse

Our approach

Decentralized Free/disposable IDs Enhances privacy Should discourage

misuse

Our approach

4

Our approachOur approach

Design principle Users form a club that relies on indirect

service reciprocity

Distinct characteristics Fully decentralized No user registration Designed with off-the-shelf equipment in

mind Does not assume altruists

Design principle Users form a club that relies on indirect

service reciprocity

Distinct characteristics Fully decentralized No user registration Designed with off-the-shelf equipment in

mind Does not assume altruists

5

EntitiesEntities

Peer: provides service via home AP, consumes when mobile

Peer ID: uncertified public/private key pair

Accounting unit: digital receiptSigned by roaming userProof of transaction

Receipt repositories

Peer: provides service via home AP, consumes when mobile

Peer ID: uncertified public/private key pair

Accounting unit: digital receiptSigned by roaming userProof of transaction

Receipt repositories

6

Receipts and the reciprocity algorithm

Receipts and the reciprocity algorithm

Consuming member CertificateConsuming member Certificate

TimestampTimestamp

Member SignatureMember Signature(Signed with member private key)(Signed with member private key)

Weight (amount of bytes relayed)Weight (amount of bytes relayed)

Contributor Public KeyContributor Public Key Receipt generation

AP periodically requests fresh receipt

Roamer sends signed receipt

Storage Receipt repositories Input to the reciprocity

algorithm

Algorithm output Indirect Normalized Debt

(IND) Translated to QoS

Receipt generation AP periodically requests

fresh receipt Roamer sends signed

receipt

Storage Receipt repositories Input to the reciprocity

algorithm

Algorithm output Indirect Normalized Debt

(IND) Translated to QoS

7

Can it scale?Can it scale?

8

The locality of visitsThe locality of visits

Visits to foreign areas are rare

IND ≈0Receipts are

unvalued in foreign areas

Visits to foreign areas are rare

IND ≈0Receipts are

unvalued in foreign areas

9

A Super-Peer-assisted architecture

A Super-Peer-assisted architecture

At least one Super Peer per Area

Super Peers:• Globally known

• Trusted

• Without extra computational capabilities

10

An algorithm for large-scale roaming - Specification

An algorithm for large-scale roaming - Specification

The algorithm should run for all transactions (not only for roaming ones) Low Complexity As few Super Peers as possible Super peers should be used only when

necessary

Incentive based Normal users

To contribute service to Super Peers To contribute service to roamers

Super Peers To mediate other transactions

The algorithm should run for all transactions (not only for roaming ones) Low Complexity As few Super Peers as possible Super peers should be used only when

necessary

Incentive based Normal users

To contribute service to Super Peers To contribute service to roamers

Super Peers To mediate other transactions

11

P2PWNC AREA

ExampleExample

Green Team

HOME P2PWNC AREA

Team Server

Home Super Peer

Team Server

A user visits a foreign areaHe asks service from an AP and informs the AP about the SP of his home area

Visited Super Peer

Team Server

Team Server

The team server runs the reciprocity

algorithm

According to the result he should not contribute service. So, he asks the SP of his home location

to find a guarantor, in order to provide service to the user

Simultaneously asks from the user’s home location SP to calculate the same quantity and

the waits for the answer.

The VSP runs the reciprocity algorithm for

the prospective consumer, in order to calculate the quantity (IND) that he is able to

guarantee.

The HSP runs the reciprocity algorithm in order to calculate

the IND for the prospective consumer

Informs the VSP for the calculated IND

VSP calculates:1. The final IND for the

prospective consumer. 0,2xIND (VSP) + 0,8xIND(HSP)

2. The guarantor SP for this transaction.

Informs the HSP (guarantor) and the Team Server of the provider about the IND calculated

AP asks receipts from the SP for his own use and also from the consumer on behalf of the SP

The consumer signs receipts to the SP and the SP signs receipts to the AP

12

Everyone is happy!Everyone is happy!

Roaming users have consumed service

The AP has gained the valuable receipts of the SP

The SP helped a member of his area and paid off his debt

Roaming users have consumed service

The AP has gained the valuable receipts of the SP

The SP helped a member of his area and paid off his debt

13

SimulationsSimulations

Input Parameters Server Repository Size Client Repository Size Users Number

Areas Number Area Population

Roaming probability Number of stay rounds in

the foreign area(stop over rounds)

Contribution of the super peers to IND

Number of super peers per area

Input Parameters Server Repository Size Client Repository Size Users Number

Areas Number Area Population

Roaming probability Number of stay rounds in

the foreign area(stop over rounds)

Contribution of the super peers to IND

Number of super peers per area

Output Parameters SW Hit Ratio Requests to the super

peers Super peers

guarantees

Output Parameters SW Hit Ratio Requests to the super

peers Super peers

guarantees

14

Number of Regions EffectNumber of Regions Effect

Number of Regions effect on Hit ratio

0%10%20%30%40%50%

60%70%80%90%

100%

0 2 4 6 8 10 12 14 16 18 20 22

Number of Regions

Ave

rag

e H

it r

atio

NORMAL

ROAMERS

NORMAL w ith Super Peers

ROAMERS w ith Super Peers

Input Parameters

Patience=20 (rounds)

Server Repository Size=2000 (receipts)

Client Repository Size=300 (receipts)

Number of peers=1000 (2x500 - 4x250 - 8x125 - 10x1000 - 20x50)

Roaming Start Round=5

Roaming Probability p=0.1

Stop Over Rounds=1

Super peers Participation=80% consumer part. - 20% provider part.

Super Peers per Region=1

Number of Regions effect on SW

0123456789

10

0 2 4 6 8 10 12 14 16 18 20 22

Number of Regions

Ave

rag

e S

W p

er M

atch

NORMAL

ROAMERS



15

Server Repository Size EffectServer Repository Size Effect

Server Repository Size effect on Hit Ratio

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

1000

1250

1500

1750

2000

2250

2500

2750

3000

Server Repository Size (receipts)

Ave

rag

e H

it r

atio

NORMAL

ROAMERS



Server Repository Size effect on SW

0

1

2

3

4

5

6

7

8

9

10

1000

1250

1500

1750

2000

2250

2500

2750

3000


Ave

rag

e S

W p

er M

atch

NORMAL

ROAMERS



Input Parameters

Patience=20(rounds)

Server Repository Size=1000 (250) 3000

Client Repository Size=250

Number of peers=1000 (4x250)

Roaming Start Round=5

Roaming Probability p=0.1

Stop Over Rounds=1

Super peers Participation=80% consumer part. - 20% provider part.

Super Peers per Region=1

Server Repository size effect on Super Peers Usage

0%

20%

40%

60%

80%

100%

0 500 1000 1500 2000 2500 3000 3500


ratio

(%)

Super peers requests

Super peers help

16

Participations of super peers in the IND result

Participations of super peers in the IND result

Input Parameters

Patience = 20 (rounds)

Repository size = 2000 (receipts)

Receipts to merge = 300

Number of Peers = 1000 ( 4x250) - (20x50)

Roaming Start Round = 25

Roaming Probability p = 0.1

Stop Over Rounds = 1

super peers participation=variable

Super Peers per Region = 1

Home Super Peer Participation effect on SW

0

2

4

6

8

10

0% 20% 40% 60% 80% 100%

Home SP Participation

Ave

rag

e S

W p

er M

atch

NORMAL ROAMERS

Home Super Peer Participation Effect on Hit Ratio

95%

96%

97%

98%

99%

100%

0% 20% 40% 60% 80% 100%

Home SP participation

Ave

rag

e re

qu

est/

con

sum

e ra

tio

%



17

The effect of the number of super peers per region

The effect of the number of super peers per region

Input Parameters




Number of Peers = 1000 ( 8x125)




super peers participation (Home - Visited)=80% - 20%

Super Peers per Region = 1,2,3

Super Peers per Region effect on SW

0

2

4

6

8

10

0 1 2 3 4

Super Peers Per Region

Ave

rag

e S

W p

er M

atch

NORMAL ROAMERS

Super Peers per Region Effect on Hit Ratio

80%

85%

90%

95%

100%

0 1 2 3 4

Super Peers Per Region

Ave

rag

e H

it r

atio



18

Scale EffectScale Effect

Scale effect on Hit Ratio

50%

60%

70%

80%

90%

100%

0 2000 4000 6000 8000

Number of Peers

Ave

rag

e H

it R

atio

Series1 Series2

Scale Effect on SW

0

2

4

6

8

10

0 2000 4000 6000 8000

Number of Peers

Ave

rag

e S

W p

er M

atch

Series1 Series2

Input Parameters




Number of Peers = (4x250) (10x250) (20x250) (28X250)




super peers participation (Home - Visited)=80% - 20%

Super Peers per Region = 1

19

THE ENDTHE END

Thank you!Thank you!

Documents

Exploiting super peers for large-scale peer-to-peer Wi-Fi roaming